Refactoring getHostIdentifier and adding some extra logging

Example output from INFO log:

```
[marpaia-mbp] osquery (host-ident-sig) * tail -f /var/log/osquery/osqueryd.INFO
I1125 08:47:03.676038 137199616 scheduler.cpp:69] Executing query: select * from time;
I1125 08:47:03.681260 137199616 scheduler.cpp:107] Found results for query time for host: marpaia-mbp.local
I1125 08:47:04.683869 137199616 scheduler.cpp:69] Executing query: select * from time;
I1125 08:47:04.693099 137199616 scheduler.cpp:107] Found results for query time for host: marpaia-mbp.local
I1125 08:47:05.695508 137199616 scheduler.cpp:69] Executing query: select * from time;
I1125 08:47:05.700830 137199616 scheduler.cpp:107] Found results for query time for host: marpaia-mbp.local
```